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The performance and emission of spark ignition engines are optimized using combustion characteristics. The flame characteristics such as flame kernel growth rate, flame speed, flame development angle, rapid burning angle, over all burning angle and drift velocity influence the combustion process of SI engines. In this direction, experiments were conducted to measure flame kernel growth rate in AVL research spark ignition engine using AVL VISIO FEM instrument. The flame kernel growth rate measured at different engine speeds and spark timing. The measured flame kernel growth rate for gasoline fuel was in the range of 4 to 6 m/s. It was observed from the results that flame kernel growth rate is the highest at MBT spark timing. The effects of flame kernel growth rate on performance and emission characteristics were analyzed in detail. Brake thermal efficiency increases with the increase of flame growth rate. CO emission is good agreement with the kernel growth rate.

In this study some experiments were carried out to evaluate fuel consumption and exhaust emissions of carbon monoxide (CO), oxides of nitrogen (NOx)) and hydrocarbons (HC) with compressed natural gas (CNG) and gasoline in a single cylinder engine. Compressed natural gas showed 3 to 5 percent higher thermal efficiency and 15 percent lower specific fuel consumption as compared to gasoline. Also CO emissions were lower by 30-80 percent in rich zone and NOx by about 12 percent at an equivalence of 1.0. At wide open throttle CNG operation resulted in 10 to 12 percent lower power output. However, thermal efficiency and brake specific fuel consumption (bsfc) was better with CNG as compared to gasoline. Dual spark plug operation increased power output by 3 to 5 percent.